This invention relates to skeletal isomerization of olefins, i.e., to the reorientation of the molecular structure in respect to the formation or elimination of side chains. This invention more particularly relates to the conversion of unbranched olefins into branched olefins having the same number of carbon atoms.
Skeletal isomerization of olefins is known to be accomplished by contacting unbranched or lightly branched olefins with acidic catalysts at elevated temperatures. The process is generally applicable to the isomerization of olefins having about 4 to about 20 carbon atoms and is especially applicable to olefins having about 4 to about 10 carbon atoms per molecule. The process may be used to form isobutene from normal butenes, methyl pentenes and dimethyl butenes from normal hexenes, and so forth.
Known skeletal isomerization catalysts include aluminas and halogenated aluminas, particularly F- or Cl-promoted aluminas. Supports employed in such catalysts are either alumina or predominantly alumina due mainly to the high acidity of alumina. See Choudary, V. R., "Fluorine Promoted Catalysts: Activity and Surface Properties", Ind. Eng. Chem., Prod. Res. Dev., 16(1), pp. 12-22 (1977) and U.S. Pat. No. 4,400,574.
An object of this invention is an improved process for the skeletal isomerization of olefins, especially for the isomerization of n-butenes to form isobutene. A more specific object is an easily prepared, stable, active and selective isomerization catalyst and process for skeletal isomerization of olefins. Other objects and advantages of the invention will be apparent from the following description.